Flanges Stiffer on Rebuilt Transmission?

arbita1 · arbita1's Garage

I rebuilt a transmission a few years ago with the help of many on this board. Im finally getting around to installing it. To be honest, despite all the help i received, I'm still a bit aprehensive about my rebuild. So upon removal, I started comparing the old transmission to the rebuilt one.

The first thing I compared was the shift rod feel. And it feels basically the same on both. Actually the rebuilt one has a more solid sound when i rotate it back and forth as the shift fork selector is moving around inside.

The next thing I compared was the feel of the flanges. I notice that the rebuilt transmission flanges rotate more stiffly than the old transmission. Is this a cause for concern? I'm very worried about preload.

Oh Haha · 10-14-2011, 04:02 AM

Rebuilt gearboxes WILL feel stiffer until you get some miles on the bits.

You should use a break-in gear lube for a few hundred miles and then switch it out for whichever brand you normally use.

Matt Monson · 10-14-2011, 05:50 AM

I would expect that there would be more preload on new carrier bearings than on old tired ones. However, did you reset the ring and pinion? Or was it just fresh carrier bearings? If it's a new ring and pinion installation you would want to be sure to measure both the ring gear backlash and the bearing preload with the proper tools. If you didn't you're just taking a shot in the dark with it.

arbita1 · arbita1's Garage

Quote:

Originally Posted by Matt Monson

I would expect that there would be more preload on new carrier bearings than on old tired ones. However, did you reset the ring and pinion? Or was it just fresh carrier bearings? If it's a new ring and pinion installation you would want to be sure to measure both the ring gear backlash and the bearing preload with the proper tools. If you didn't you're just taking a shot in the dark with it.

The ring and pinion were the original in the transmission and not replaced. The only thing I replaced were the bearings. Pete Z had advised at the time that if everything was original, then I should be okay with no differential adjustments.

sc_rufctr · 10-14-2011, 06:41 AM

Bang it in there and drive the sucker.

KTL · 10-14-2011, 06:50 AM

Here's a stupid question......... is it filled with oil? If your rebuilt trans is still dry and hasn't had oil splashed thru it, it's certainly going to be a bit stiffer to turn.

Peter Zimmermann · 10-14-2011, 07:54 AM

Quote:

Originally Posted by arbita1

The ring and pinion were the original in the transmission and not replaced. The only thing I replaced were the bearings. Pete Z had advised at the time that if everything was original, then I should be okay with no differential adjustments.

Other than setting the carrier bearing pre-load, which must be done with new bearings.

From my post #70...

The oil on the o-ring is only for ease of assembly. Just be warned that in many transmissions the pre-load will change over time due to normal stresses, and should be checked.

From your thread...

915 Rebuild (Part II) - Time for Assembly

There was quite a bit of discussion regarding you not being able to turn your installed diff, finding a casting flaw, possibly having shims installed wrong, etc. It was established that you had replaced SKF bearings with new SKFs, and I posted photos of how to make a diff-lock washer to fit on an axle flange, along with advice regarding the best torque wrench to buy to verify carrier bearing pre-load.

When it's all said & done, diff flanges will turn more tightly after carrier bearing replacement, but if you did not verify the pre-load you are at risk to have a problem; it's not possible to really know. Unfortunately, to set pre-load the gear cluster must be removed in order to separate the pinion head from the ring gear.

KTL · 10-14-2011, 08:08 AM

Pete,

With respect to diff side bearing preload, I understand the need to separate the connection between the diff and the pinion so as to avoid the influence on preload by the pinion shaft. However, could a substitute method be the removal of the ring gear from the diff? Seems that removing the ring gear would accomplish the same need- disconnect the diff from the pinion shaft.

arbita1 · arbita1's Garage

KTL - No, there is no gear oil in the transmission yet.

Pete, I was reviewing your tutorial this morning to see if you had a procedure for checking preload without buying the special tools. I didn't find anything. Do you happen to have one?

Peter Zimmermann · 10-14-2011, 08:43 AM

Quote:

Originally Posted by arbita1

KTL - No, there is no gear oil in the transmission yet.

Pete, I was reviewing your tutorial this morning to see if you had a procedure for checking preload without buying the special tools. I didn't find anything. Do you happen to have one?

Matt, check post #46 in your thread linked to in post #7 of this thread. Everything is there, including measurements for the washer used to lock the diff to turn it. You must have the washer and an inch/lb torque wrench.

FYI; I would not consider removing the ring gear in order to set pre-load, way to much work. I think that removing the pinion shaft is easier!

arbita1 · arbita1's Garage

Got it. Now once I obtain a washer and inch torque wrench, i think i understand how the washer is installed behind the flange. But then what?

Peter Zimmermann · 10-14-2011, 11:45 AM

Quote:

Originally Posted by arbita1

Got it. Now once I obtain a washer and inch torque wrench, i think i understand how the washer is installed behind the flange. But then what?

Tutorial Part 5! Read through it a couple of times and it will start to make sense...

Porsche Wiki

arbita1 · arbita1's Garage

Quote:

Originally Posted by Peter Zimmermann

Tutorial Part 5! Read through it a couple of times and it will start to make sense...

Porsche Wiki

Ok. I read your tutorial as well as the factory manual. And I do believe I understand it more or less. Here's the problem. From what I can tell, preload needs to be measured with the pinion shaft disengaged. My transmission is complete already. Can I still take a measurement and account in some way for the pinion shaft?

arbita1 · arbita1's Garage

Quote:

Originally Posted by arbita1

Ok. I read your tutorial as well as the factory manual. And I do believe I understand it more or less. Here's the problem. From what I can tell, preload needs to be measured with the pinion shaft disengaged. My transmission is complete already. Can I still take a measurement and account in some way for the pinion shaft?

Oops. I just saw you and KTL already discussed this above.

Peter Zimmermann · 10-14-2011, 12:37 PM

Quote:

Originally Posted by arbita1

Ok. I read your tutorial as well as the factory manual. And I do believe I understand it more or less. Here's the problem. From what I can tell, preload needs to be measured with the pinion shaft disengaged. My transmission is complete already. Can I still take a measurement and account in some way for the pinion shaft?

Nope. Sorry!

arbita1 · arbita1's Garage

Wow. I wish I understood this better when I was rebuilding the transmission.

Now as far as removing the ring gear being more work to removing than the pinion shaft. I'm not exactly sure what's involved in removing the ring gear, but isn't removing the pinion shaft basically taking the transmission completely apart again...excluding dissembling the gear stacks?

I can't take this transmission apart again right now. I don't have the time and I have to get my car back up and running. So my options I think (if removing the ring gear is not viable), is to put my old transmission back in and wait until I get more time to deal with this, or put in the new transmission and hope for the best.

Now, if I do the latter and the preload is not good what will be the symptoms? How will I know if it's good or bad? And what can happen if I drive the car that way?

Peter Zimmermann · 10-14-2011, 02:30 PM

Quote:

Originally Posted by arbita1

Wow. I wish I understood this better when I was rebuilding the transmission.

Now as far as removing the ring gear being more work to removing than the pinion shaft. I'm not exactly sure what's involved in removing the ring gear, but isn't removing the pinion shaft basically taking the transmission completely apart again...excluding dissembling the gear stacks?

I can't take this transmission apart again right now. I don't have the time and I have to get my car back up and running. So my options I think (if removing the ring gear is not viable), is to put my old transmission back in and wait until I get more time to deal with this, or put in the new transmission and hope for the best.

Now, if I do the latter and the preload is not good what will be the symptoms? How will I know if it's good or bad? And what can happen if I drive the car that way?

If, somehow, you made a mistake with the bearings/shim placement, it's possible that your backlash is either too tight, or too loose. Too tight could destroy your ring & pinion very quickly, and too loose might cause it to slap, which might be audible on accel to decel, or decel to accel.

If you can turn your flanges using your bare hands the pre-load might be close, or even correct, but I can't say for sure. I thought that I've had the pre-load correct in transmissions, only to find out when doing the measurement, that I was a little tight or a little loose. I'm not really sure what could happen, for instance, if your pre-load is on the high side of the spec for an FAG bearing, but you're using SKFs. I've never been able to learn why the pre-load spec is higher on the FAG product, so it's really a crap-shoot.

What I am certain of is that long-life can only be guaranteed with precise measurements.

arbita1 · arbita1's Garage

Thanks Pete for for all your helpful insight...again.

I have some time to think about it. I have to finish my SSI installation (which entails drilling out a broken exhaust stud) and new clutch installation. So once I'm done with that, hopefully I've decided what to do.

I looked at the factory manual and see why you say it's a pain to remove the ring gear. I guess it's a tight fit and it has to be heated and aligned with a "home made pin" to reinstall. Although, in truth that seems less of a pain in my mind than taking the transmission apart all over again.

I'll update once I've decided.

Peter Zimmermann · 10-14-2011, 04:07 PM

I'm thinking about the easiest way to do the measurement. How about if you remove the nose cover, the castle nut and pinion nut (you'll have to get a replacement), and 5th/R components. Pull the 5/R shift fork/shaft past its detent and you won't have to re-adjust it later (but check it anyway!).

Remove the center housing and fork plate, remove the 1/2 shift fork bolt and the six nuts/washers that hold the P/S clamping plate and the four nuts/washers for the M/S clamping plate. Remove the upper detent plug, spring and detent, and slide the gear cluster back (out) about the width of fourth gear, which should be enough to get the pinion head away from the ring gear. The 3/4 shift fork/rod will move with the cluster, and the 1/2 fork will slide on its rod. (I realize that you'll have to buy three new gaskets (for the center housing, the fork plate, and the nose cover, but you won't need a kit - the gaskets can be bought separately).

Turn the trans on its side and make your pre-load measurement using your big washer and torque wrench. Make sure that your socket set has an adapter to connect your 1/8" drive wrench to a 3/8" socket (unless your torque wrench is 3/8" drive, of course)!

I'm thinking that if you remove the ring gear you will need to buy a set of lock plates, and you probably should be prepared to measure/set backlash after it's back together because you want to be sure that the ring gear is flat against its mounting surface.